The present invention relates to an installation for the extraction of fluid from an expanse of water, comprising:                an upper structure extending at least in part above the surface of the expanse of water;        at least one flexible hose extending through the expanse of water, the flexible hose comprising a head for connection to a collector placed on the upper structure, the flexible hose being capable of moving through the expanse of water between an upper configuration in which it is connected to the collector and a lower disconnected configuration.        
An installation of this type generally comprises a floating structure such as a platform disposed above the expanse of water and a plurality of risers which connect the heads of wells located at the bottom of the expanse of water to the floating structure.
An installation of this type is intended, for example, for the extraction of deposits of hydrocarbons located under the bottom of an expanse of water such as a lake, a sea or an ocean, under conditions in which a stoppage of production and rapid safeguarding of the extraction installation may be required.
These conditions are encountered, in particular, in regions where the expanse of water is temporarily or permanently covered by a layer of ice, such as the polar regions, in particular the artic region.
In these regions, the layer of ice present at the surface of the expanse of water is relatively mobile. It can therefore partially damage the floating structure if said structure is anchored to the bottom of the expanse of water.
To overcome this problem, there are known installations equipped with ice-breakers which are set into rotation about the floating structure to keep the floating structure in an acceptable state for extraction.
It is also known to break the ice locally round the floating structure, for example by using a floating column-type platform with a median constriction, by vertically moving the floating structure to break the ice round the median constriction.
However, if the atmospheric conditions become too difficult or if a large-volume ice mass such as an iceberg moves towards the installation, this installation must be secured very quickly. Flexible hoses are accordingly disconnected at a distance from the floating structure, and the floating structure is moved from its extraction position to an evacuation position in safer waters.
These icebergs may have a very deep draft, e.g higher than 100 meters. When an iceberg is stuck in a layer of packed ice, it may be difficult to detect. Most of the time, it is not possible to change their route.
Under unfavorable weather conditions, the detection of icebergs is done by acoustic means, such as sonar. Due to the limited range of detection of sonars, an iceberg may be relatively close to the installation when it is positively detected. As a consequence, the installation must be able to perform an extremely quick disconnection of the risers, e.g. in fifteen minutes, to allow the upper floating structure to be moved away from the iceberg route. Moreover, once the iceberg is away from the installation, the reconnection of the risers must be fast and efficient to put back the installation into production in the shortest time possible.
For rapidly disconnecting flexible hoses at a distance from the floating structure, EP-A-1 849 701 for example discloses an installation of the aforementioned type comprising a shuttle formed by a riser top body which joins the connection heads of a plurality of flexible hoses.
The shuttle is mounted ejectably on a deck which externally extends the floating structure opposite and at a distance from the expanse of water. Under normal extraction conditions, the shuttle is fixed on the deck extending the structure and the flexible hoses are connected to collectors located on this deck.
In an emergency, the shuttle carrying the connection heads is ejected downwards from the deck and thus falls freely into the expanse of water, releasing the flexible hoses towards their disconnected configuration.
A solution of this type is partially satisfactory in quickly safeguarding the installation. However, there is a very high risk that the flexible hoses will be damaged during the descent.
Indeed, in EP-A-1 849 701, the shuttle carrying the connection heads drops in free fall until it reaches its equilibrium position in water, in which the buoyancy of the shuttle compensates its own weight, the weight of the risers hoses and the weight of the mooring lines.
When it free falls, the shuttle has a strong tendency to fall beyond its equilibrium depth and to oscillate vertically with strong amplitude before reaching equilibrium. Until the equilibrium position is reached, there is a strong risk of damaging the riser hoses, due to excessive bends, impact between different hoses, impact with mooring lines or with the bottom of the water expanse when the water depth is relatively low, e.g. in the range of 300 to 400 m.
Moreover, the shuttle will be difficult to locate, once disconnected, and this can delay the return to operation of the installation. Strong lifting means may be necessary to lift back the shuttle to its reconnection position near the surface, since this position is quite far up from the equilibrium position.
The overall weight of the assembly formed by the mooring lines, the flexible hoses and the shuttle is high which necessitates a corresponding dimensioning of the upper floating structure, hence increasing manufacturing and settling costs of the installation.
WO 93/24733 discloses an installation comprising a floating vessel connected with releasable means to a floating turret. The floating turret is located very close to the surface to be inserted in a moon pool of the floating vessel when the upper vessel is connected.
In case an iceberg threatens the installation, the vessel can be disconnected and moved rapidly away from the turret. However, once disconnected from the vessel, the turret floats nears the surface and thus may be impacted by icebergs.